Steve, Ricki and Paul are still haunted by the disappearance of their sister Cheryl.

In 2016, Wollongong detective Frank Sanvitale was handed a cold case and asked to look into it. It was a case he knew well, as most people in the Illawarra region did.

"I knew how old the case was I'm like a dog with a bone and when I picked it up I couldn't let it go," he said.

He teamed up with fellow detective Damian Loone and they went through boxes of material, which included a dusty confession from 1971.

It was made by a 17-year-old runaway who came forward to confess to the abduction and murder of Cheryl.

"I come around the front of the pavilion behind her and grabbed her," the man told police at the time.

"There was some bloke sitting on the wall in front of the pavilion so I had to put my hand over her mouth to stop her screaming because if she had of screamed he would have heard it.

"I went over the big drain and stayed in the scrub area and got near a creek near the main road. I tied a handkerchief and a shoelace around her mouth to stop her screaming and with the other shoelace I tied up her hands.

"I was going to have sexual intercourse with her … she started to scream as soon as I took the gag off her.

"I put my hands around her throat and told her to shut up. I guess I must have strangled her. She stopped breathing and stopped crying and I thought she was dead, so I panicked and covered her up with bushes and run for it."

Cheryl's body has never been found.

Wollongong detective Frank Sanvitale was handed the cold case in 2016 and found the stunning confession that had been ignored in 1971.

Cheryl Grimmer disappeared from a Fairy Meadow beach near Wollongong in 1970.

60 Minutes tracked down one of the original investigators who took the confession from the man, who admitted he thought the claim was credible.

But the officer in charge wasn't convinced, believing the teenager was making up the tale for attention, so the junior officer went along with the decision.

The two detectives who took on the cold case were able to corroborate several key details from the man's 1971 confession, including his description of landmarks and the what Cheryl had been wearing down to features of the patch of farmland where he claims to have left her body.

Cover of the Daily Mirror newspaper.

Chillingly, the man also described in his confession seeing Ricki lift Cheryl up to have a drink from a water bubbler outside the change sheds.

"I don't remember the asking for a drink. I could just see she wanted a drink so I just helped her up. It's surreal … he was there watching, waiting. Waiting for his opportunity."

"He says, 'What do you need to speak to me about?' And I said, 'You tell me'. There was a very long pause. then he says to me, 'It's something I did when I was very young which I regret every day of my life'.

"He said those words to me. It's in my statement. And then he says, 'Is it about a young girl at Fairy Beach?' He didn't use Fairy Meadow, he just said Fairy, I remember that."

The brothers were devastated to discover a confession had been made and that the family was never told.

The man met with the two cold case detectives at a police station in Victoria but he insisted he had never been to the beach.

After questioning, he was arrested and charged with Cheryl's murder and extradited to New South Wales to appear in court.

The man, who cannot be identified, pleaded not guilty and was held on remand awaiting trial, scheduled for May this year.